Embryonic diapause in the European roe deer (Capreolus capreolus)

Abstract

The first written reports on embryonic diapause in the European roe deer (Capreolus capreolus) date back to 1843 and 1854. While the rut takes place in July/August, rapid embryo elongation and implantation take place in December/January, after a five month period of embryonic diapause. The post-implantation development lasts another five months and an average of two fawns are born in May. As fertilization and subsequent implantation are decoupled, the roe deer offers the opportunity to study changes in hormones, embryonic and endometrial morphology and transcriptome dynamics, as well as the uterine microenvironment in a high time-dimension. So far, it has been shown that peripheral increases in prolactin, estradiol-17β and progesterone are a consequence, rather than the cause of reactivation of embryo development. Increased uterine secretions and the presence of embryonic cell organelles coincide with embryo elongation. This suggests that the "quiet embryo" hypothesis might hold for diapausing embryos. The factors controlling embryonic developmental pace in the roe deer are yet to be identified. We propose a multi-omics approach to determine the temporal molecular changes during diapause, prior to embryo elongation, which morphologically marks the reactivation of embryo development, and upon elongation. Thereby, we will obtain insights into the molecular mechanisms and environmental cues that inhibit and drive cell proliferation. By data integration, we aim at identifying the origin of the factors associated with reduced embryonic developmental pace. The knowledge of a species-independent mechanism driving embryo development past the blastocyst stage is of high interest to reproductive biologists and for species conservation programs.